I am trying to design a remote kill switch for a childs motorcycle that a parent could control from a remote location. I have a (i believe) a uhf car starter/ alarm with several functions. What I need this device to do is, when activated will close a remote circuit to ground, thus killing the motor, and open to allow for restart. The signals coming from the receiver are millivolts. MY question is I need some sort of relay that will operate under millivolts to open or close the desired circuit. I have a PRMA2A05 reed relay, but cannot get it to work until the voltage is >3.0 volts. Can I make this relay work or is there another alternative. My knowledge of electronics is very intermediate at best. Any suggestions would be appreciated.

Thanks for the advise. I am able to switch 5v on and off from remote, however I am having difficulty getting that voltage to trigger a relay. I have gone to JS1-5v relay and I believe I am energizing the coil but with no results. Can you help?

Without having your circuit to look at, I can only guess at an answer.

Your remote puts out a radio-frequency carrier. This is AC in nature. A 5 volt relay coil wants to see DC. The 5 volt rating means that 5 volts across the coil will push enough current through the coil to make it a small electromagnet. The magnetism will pull a metallic armature and close a pair of contacts. Even is rectified, your remote's carrier is unlikely to supply the current necessary to energize the relay coil.

I think a child's motorcycle is very nearly an oxymoron. Says me, if you need a kill switch the the child is not ready for it. Wouldn't it be easier to wait until he is ready and teach him/her to use it properly. What are you thinking?

If the +5 volts is working it may not have enough current to do the job. You may need to use a transistor to boost it's effect. We do need a schematic, preferably in gif or jpeg to see what is going on.

Thanks for your feedback. Yes I agree on the oxymoron. The motorcycle is actually my neighbours 50cc quad he bought for his 3 yr old. On my advise I suggested to him a kill switch. The rf device was an old car alarm system my son had. I managed to find a 5v source from the darlington transistor on it to trigger the relay and thus close the circuit to ground. My testing methods to energise the relays coil wasn't correct. After discovering this, I was able to use the PRMA2A05 reed relay. I now have a happy , albeit overanxious neighbour. As for a schematic, I am not good at those, but I would gladly help other hobbiests on this project if they are interested. I am new to this forum and wish to learn more. I am sure you will be hearing from me again. Thanks for all the feedback.

One more consideration for that kill switch, the best solution is for the kill switch to activate if the unit goes out of range, this way when the child is headed out of range instead of discovering that the kill switch doesn't work while the neighbor's son is headed for your mercedes SL500, the motorcycle is shutdown when it goes out of range.

The only difficulty with killing the engine if it gets out of range is that the remote control transmitter would need to operate continuously; loss of signal=ignition disable. Your transmitter would eat a lot of batteries that way although it would be safer.

Papa Bravo the guy wasn't looking for a lecture he was asking for some help. THis activity with the safety switch is far safer than skiing that my boy is doing at 4! I was however thinking of a recoiling tether like they use for dog leashes...to avoid those trees! Learning any skill has its risks at any age and wize parents can reduce those risks.

20 years ago I saw video of a child die as a result of losing control of a go-kart and driving under a pickup truck so I have had the same idea for children learning any motor sport SOme of the top F1 drivers started racing mini carts when they where around 5...this safety feature is an exellent idea for responsible parents.

IF you are using an auto related alarm you just have to use a Bosh style 30A relay. All the 500ma transistor outputs from alarms are 12v (ish). Only high end units will have a "latched" output that would keep the relay energized (provided you have a battery source for the unit)....better idea as Off road vehicles usually don't have a battery so here is my suggestion. Use the trunk pop output from the alarm and connect it to a door lock actuator. Mechanically hook up the door lock actuator to a toggle or blade swich that will interrupt power to the ignition. That way there is still residual power as the engine is coming to a halt to make sure the brain can throw the switch. It should happen instantly anyways. You will have to manually re-set the switch every time but since there is no power once the engine quits then you would anyways.